Focus Control Amount Determination Apparatus, Method, and Imaging Apparatus

1. A focus control amount determination apparatus, comprising: a detection means for detecting a predetermined structure within a subject from inputted image data obtained through digital conversion of an image of the subject generated on an imaging surface, formed of an image sensor, by focusing the light from the subject through an imaging optical system; a parameter obtaining means for obtaining a sharpness parameter that represents a weighting value for a statistical characteristic amount representing a sharpness level of the structure by applying the structure detected by the detection means to a model, which represents the structure by means of: one or more statistical characteristic amounts, including the statistical characteristic amount representing the sharpness level of the structure, obtained by performing a predetermined statistical processing on image data representing a plurality of images that represent the predetermined structure in different sharpness levels; and a weighting parameter for weighting each of the statistical characteristic amounts according to each of the characteristics of the structure; and a control amount determination means for determining the focus control amount for the imaging optical system such that the structure within the subject of the image is brought into focus according to the obtained value of the sharpness parameter.

2. The focus control amount determination apparatus according to claim 1 , wherein the control amount determination means comprises: a storage section for storing information indicating the correlation between the values of the sharpness parameter and focus control amounts of the imaging optical system; and a control amount obtaining means for obtaining a focus control amount corresponding to the value of the sharpness parameter obtained by the parameter obtaining means based on the correlation information stored in the storage section.

3. The focus control amount determination apparatus according to claim 1 , wherein: the apparatus further comprises a selection means for selecting a model from a plurality of models, each representing the predetermined structure with respect to each attribute; and the parameter obtaining means is a means for obtaining the sharpness parameter by applying the structure to the selected model.

4. The focus control amount determination apparatus according to claim 1 , wherein the predetermined structure is a human face.

5. The focus control amount determination apparatus according to claim 1 , wherein the model and the application to the model are realized by a method employing Active Appearance Models.

6. An imaging apparatus comprising: an imaging optical system; an image sensor forming an imaging surface on which an image of a subject is focused through the imaging optical system; a conversion means for performing digital conversion on the image of the subject generated on the imaging surface; the focus control amount determination apparatus according to claim 1 ; and a means for controlling the focus of the imaging optical system according to the control amount determined by the focus control amount determination apparatus.

7. The imaging apparatus according to claim 6 , wherein the control amount determination means comprises: a storage section for storing information indicating the correlation between the values of the sharpness parameter and focus control amounts of the imaging optical system; and a control amount obtaining means for obtaining a focus control amount corresponding to the value of the sharpness parameter obtained by the parameter obtaining means based on the correlation information stored in the storage section.

8. The imaging apparatus according to claim 6 , wherein: the apparatus further comprises a selection means for selecting a model from a plurality of models, each representing the predetermined structure with respect to each attribute; and the parameter obtaining means is a means for obtaining the sharpness parameter by applying the structure to the selected model.

9. The imaging apparatus according to claim 6 , wherein the predetermined structure is a human face.

10. The imaging apparatus according to claim 6 , wherein the model and the application to the model are realized by a method employing Active Appearance Models.

11. A focus control amount determination method comprising the steps of: detecting a predetermined structure within a subject from inputted image data obtained through digital conversion of an image of the subject generated on an imaging surface, formed of an image sensor, by focusing light from the subject through an imaging optical system; obtaining a sharpness parameter that represents a weighting value for a statistical characteristic amount representing a sharpness level of the structure by applying the detected structure to a model, which represents the structure by means of: one or more statistical characteristic amounts, including the statistical characteristic amount representing the sharpness level of the structure, obtained by performing a predetermined statistical processing on image data representing a plurality of images that represent the predetermined structure in different sharpness levels; and a weighting parameter for weighting each of the statistical characteristic amounts according to each of the characteristics of the structure; and determining the focus control amount for the imaging optical system such that the structure within the subject of the image is brought into focus according to the obtained value of the sharpness parameter.